Portable electronics, and in particular lap top computers, have many inherent design challenges, including decreasing package size, increasing complexity, and limited power availability. Another design challenge is the elimination of excess heat that is generated by the electronics. As individual component size decreases and device complexity increases, the amount of excess heat generated in smaller areas increases. The excess heat surrounding the components can reduce the overall life of the components.
One technique used to dissipate heat near the electronic components is to incorporate a fan for directing cooling air over a warm device. However, the use of a fan to move air through a unit is not practical since considerable power is required. Therefore, there has been extensive work in developing effective methods of moving heat from the heat generating components, for example, the CPU, to a heat dissipating component, for example, a heat sink. One such method of moving heat is a heat pipe. These devices effectively move heat from one location to another within the electronic device. However, the beat, a valuable source of thermal energy, is merely dissipated away out into the atmosphere from the electrical components and discharged as waste heat.
In order to reduce power usage for increasing battery life or decreasing battery size for portable computers, design tradeoffs are often implemented to conserve power. Various devices within a portable electronic device are not considered as critical as other devices. One tradeoff commonly used is the use of LCD status displays that do not have back lights. This results in a status display that is useless in low ambient light conditions.
The LCD's using ambient light to illuminate the display are sometimes difficult to view even with high levels of ambient light. Other LCDs are illuminated from the inside so that the visibility of the displayed information is improved. As a result, some electronic devices have LCDs with back lighting. Back lighting the LCDs generally provides a more uniform image and one which is visible regardless of the level of ambient light. However, conventional back lighting requires use of additional power resources to back light the display. Furthermore, conventional lighting methods, such as LEDs, fail to illuminate a broad area of the LCD uniformly.
One approach for illuminating a liquid crystal display device is described in U.S. Pat. No. 5,453,855 issued to Nakamura et al. on Sep. 26, 1995. The '855 patent teaches back lighting an LCD device using a reflective surface in conjunction with a plurality of LEDs. The LEDs, while requiring less power than an incandescent light bulb, nonetheless consume additional system power.
Other types of electronic devices also face design challenges and solutions with respect to back lighting. For instance, electronic watches have been provided with back lighting so that the face, in some cases a liquid crystal display or an analog dial, can be viewed in low levels of ambient light. One solution for back lighting a face of the watch is to include an electroluminescent lamp. However, one of the drawbacks of an electroluminescent lamp is that it requires high voltage alternating current to drive the lamp, thereby requiring additional power from the system.
Accordingly, what is needed is a way to illuminate a display device without consuming additional system power. What is further needed is a useful manner for dissipating excess heat from system components.